SENSORY GANGLIA. CONSENSUAL ACTIONS. 333 



actions of the organs of sense, and of the nervous centres with which they are 

 connected, in animals whose movements are directly governed by the sensations 

 received through these, is followed by abnormal movements. Thus it has 

 been ascertained by Flourens, that a vertiginous movement may be induced in 

 pigeons, by simply blindfolding one eye ; and Longet has produced the same 

 effect, by evacuating the humours of one eye. These vertiginous movements 

 are more decided and prolonged, when, instead of blinding one eye, one of 

 the tubercula quadrigemina is removed; the animal continuing to turn itself 

 towards the injured side, as if rotating on an axis. The results of the experi- 

 ments of M Flourens upon the portion of the Auditory nerve proceeding to 

 the Semi-circular canals, are still more extraordinary. Section of the hori- 

 zontal semi-circular canal in Pigeons, on both sides, induces a rapid jerking 

 horizontal movement of the head, from side to side ; and a tendency to turn 

 to one side, which manifests itself whenever the animal attempts to walk for- 

 wards. Section of a vertical canal, whether the superior or inferior, of both 

 sides, is followed by a violent vertical movement of the head. And section of 

 the horizontal and vertical canals at the same time, causes horizontal and ver- 

 tical movements. Section of either canal on one side only, is followed by the 

 same effect as when the canal is divided on both sides ; but this is inferior in 

 intensity. The movements continue to be performed during several months. 

 In Rabbits, section of the horizontal canal is followed by the same movements, 

 as those exhibited by pigeons ; and they are even more constant, though less 

 violent. Section of the anterior vertical canal causes the animal to make con- 

 tinued forward somersets ; whilst section of the posterior vertical canal occa- 

 sions continual backward somersets. The movements cease when the animal 

 is in repose ; and they recommence when it begins to move, increasing in 

 violence as its motion is more rapid. These curious results are supposed by 

 M. Flourens to indicate, that the nerve supplying the semi-circular canals does 

 not minister to the sense of hearing, but to the direction of the movements of 

 the animal: but they are fully explained upon the supposition that the normal 

 function of the semi-circular canals is to indicate to the animal the direction 

 of sounds, and that its movements are partly determined by these; so that a 

 destruction of one or other of them will produce an irregularity of movement 

 (resulting, as it would seem, from a sort of giddiness on the part of the animal), 

 just as when one of the eyes of a bird is covered or destroyed, as in the ex- 

 periments just cited. 



433. But we may trace the influence of the Sensory ganglia, not merely in 

 their direct and independent operation on the muscular system, but also in the 

 manner in which they participate in all Voluntary actions. There can be no 

 doubt that, in every exertion of the will upon the muscular system, we are 

 guided by the sensations communicated through the afferent nerves, which 

 indicate to the Sensorium the state of the muscle. Many interesting cases 

 are on record, which show the necessity of this Muscular Sense, for determin- 

 ing voluntary contraction of the muscle. Thus, Sir C. Bell (who first promi- 

 nently directed attention to this class of facts, under the, designation of the 

 Nervous Circle), mentions an instance of a woman, who was deprived of it in 

 her arms, without losing the motor power; and who stated, that she could not 

 sustain anything in her hands (not even her child), by the strongest effort of 

 her will, unless she kept her eyes constantly fixed upon it; the muscles losing 

 their power, and the hands dropping the object, as soon as the eyes were 

 withdrawn from it. Here the employment of the visual sense supplied the 

 deficiency of the muscular ; but instead of being inseparably connected, as the 

 latter is in the state of health, with the action of the muscle, the former could 

 be only brought to bear by an effort of the will ; and the sustaining power was 

 therefore dependent, not upon the immediate influence of the will upon the 



